Imaging lens system

ABSTRACT

This invention provides an imaging lens system including, in order from an object side to an image side: a first lens with positive refractive power having a convex object-side surface; a second lens with negative refractive power; a third lens having a concave image-side surface; a fourth lens with positive refractive power; a fifth lens with negative refractive power having a concave image-side surface, at least one surface thereof having at least one inflection point; and an aperture stop disposed between an imaged object and the third lens. The on-axis spacing between the first lens and second lens is T12, the focal length of the imaging lens system is f, and they satisfy the relation: 0.5&lt;(T12/f)×100&lt;15.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation Application of U.S. application Ser.No. 13/433,438 filed on Mar. 29, 2012, which is a ContinuationApplication of U.S. application Ser. No. 12/654,912 filed on Jan. 8,2010, and claims priority under 35 U.S.C. 119(e) to Taiwan ApplicationSerial No. 098123694 filed on Jul. 14, 2009, the entire contents ofwhich are incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an imaging lens system, and moreparticularly, to an imaging lens system used in a mobile phone camera.

2. Description of the Prior Art

In recent years, with the popularity of mobile phone cameras, the demandfor compact imaging lenses is increasing, and the sensor of a generalphotographing camera is none other than CCD (charge coupled device) orCMOS device (Complementary Metal Oxide Semiconductor device).Furthermore, as advanced semiconductor manufacturing technology hasallowed the pixel size of sensors to be reduced and the resolution ofcompact imaging lenses has gradually increased, there is an increasingdemand for compact imaging lenses featuring better image quality.

A conventional compact lens assembly for mobile phone cameras, such asthe four lens element assembly disclosed in U.S. Pat. No. 7,365,920,generally comprises four lens elements. However, the four-element lenshas become insufficient for a high-end imaging lens assembly due to therapid increase in the resolution of mobile phone cameras, the reductionin the pixel size of sensors and the increasing demand for compact lensassemblies featuring better image quality. As there is an ongoing trendtoward compact yet powerful electronic products, a need exists in theart for an imaging lens system applicable to high-resolution mobilephone cameras while maintaining a moderate total track length.

SUMMARY OF THE INVENTION

The present invention provides an imaging lens system including, inorder from the object side to the image side: a first lens element withpositive refractive power having a convex object-side surface; a secondlens element with negative refractive power; a third lens element havinga concave image-side surface; a fourth lens element with positiverefractive power; a fifth lens element with negative refractive powerhaving a concave image-side surface, at least one surface thereof beingprovided with at least one inflection point; and an aperture stopdisposed between an imaged object and the third lens element; whereinthe on-axis spacing between the first lens element and the second lenselement is T12, the focal length of the imaging lens system is f, andthey satisfy the relation: 0.5<(T12/f)×100<15.

Such an arrangement of optical elements can effectively correct theaberrations to improve image quality of the system, reduce the totaltrack length of the imaging lens system and achieve a wide field ofview.

In the aforementioned imaging lens system, the first lens elementprovides a positive refractive power, and the aperture stop is disposednear the object side of the imaging lens system, thereby the total tracklength of the imaging lens system can be reduced effectively. Theaforementioned arrangement also enables the exit pupil of the imaginglens system to be positioned far away from the image plane, thus lightwill be projected onto the electronic sensor at a nearly perpendicularangle, and this is the telecentric feature of the image side. Thetelecentric feature is very important to the photosensitive power of thecurrent solid-state sensor as it can improve the photosensitivity of thesensor to reduce the probability of the occurrence of shading. Moreover,the inflection point provided on the fifth lens element can effectivelyreduce the angle at which the light is projected onto the sensor fromthe off-axis field so that the off-axis aberrations can be furthercorrected. In addition, when the aperture stop is disposed near thethird lens element, a wide field of view can be favorably achieved. Suchan aperture stop placement facilitates the correction of the distortionand chromatic aberration of magnification, thereby the sensitivity ofthe imaging lens system can be effectively reduced. In other words, whenthe aperture stop is disposed near the imaged object, the telecentricfeature is emphasized and enables a shorter total track length. When theaperture stop is disposed near the third lens element, the emphasis ison the wide field of view so that the sensitivity of the imaging lenssystem can be effectively reduced.

The present invention provides another imaging lens system including, inorder from the object side to the image side: a first lens element withpositive refractive power having a convex object-side surface; a secondlens element with negative refractive power; a third lens element withnegative refractive power; a fourth lens element with positiverefractive power having a concave object-side surface and a conveximage-side surface; a fifth lens element with negative refractive powerhaving a concave image-side surface, at least one surface thereof beingprovided with at least one inflection point; and an aperture stopdisposed between an imaged object and the third lens element; whereinthe on-axis spacing between the first lens element and the second lenselement is T12, the focal length of the imaging lens system is f, andthey satisfy the relation: 0.5<(T12/f)×100<15.

In the aforementioned imaging lens system, the third lens element hasnegative refractive power so that the Petzval Sum of the system can beeffectively corrected, enabling the focal plane to become more flat nearthe periphery; the fourth lens element has a concave object-side surfaceand a convex image-side surface so that the astigmatism of the systemcan be effectively corrected. Moreover, when the aperture stop isdisposed near the object side, the telecentric feature is emphasized andenables a shorter total track length. When the aperture stop is disposednear the third lens element, the emphasis is on the wide field of viewso that the sensitivity of the imaging lens system can be effectivelyreduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an imaging lens system in accordance with a firstembodiment of the present invention.

FIG. 2 shows the aberration curves of the first embodiment of thepresent invention.

FIG. 3 shows an imaging lens system in accordance with a secondembodiment of the present invention.

FIG. 4 shows the aberration curves of the second embodiment of thepresent invention.

FIG. 5 shows an imaging lens system in accordance with a thirdembodiment of the present invention.

FIG. 6 shows the aberration curves of the third embodiment of thepresent invention.

FIG. 7 is TABLE 1 which lists the optical data of the first embodiment.

FIG. 8 is TABLE 2 which lists the aspheric surface data of the firstembodiment.

FIG. 9 is TABLE 3 which lists the optical data of the second embodiment.

FIG. 10 is TABLE 4 which lists the aspheric surface data of the secondembodiment.

FIG. 11 is TABLE 5 which lists the optical data of the third embodiment.

FIG. 12 is TABLE 6 which lists the aspheric surface data of the thirdembodiment.

FIG. 13 is TABLE 7 which lists the data of the respective embodimentsresulted from the equations.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides an imaging lens system including, inorder from the object side to the image side: a first lens element withpositive refractive power having a convex object-side surface; a secondlens element with negative refractive power; a third lens element havinga concave image-side surface; a fourth lens element with positiverefractive power; a fifth lens element with negative refractive powerhaving a concave image-side surface, at least one surface thereof beingprovided with at least one inflection point; and an aperture stopdisposed between an imaged object and the third lens element; whereinthe on-axis spacing between the first lens element and the second lenselement is T12, the focal length of the imaging lens system is f, andthey satisfy the relation: 0.5<(T12/f)×100<15.

In the aforementioned imaging lens system, the first lens element haspositive refractive power and a convex object-side surface so that thetotal track length of the imaging lens system can be effectivelyreduced; the second lens element has negative refractive power so thatthe chromatic aberration of the system can be favorably corrected; thethird lens element may be a lens element with either negative orpositive refractive power; the fourth lens element has positiverefractive power so that the positive refractive power of the first lenselement can be effectively distributed to reduce the sensitivity of theimaging lens system; the fifth lens element with negative refractivepower and the fourth lens element with positive refractive power form atelephoto structure, thereby the total track length of the imaging lenssystem can be effectively reduced. When the third lens element hasnegative refractive power, the Petzval Sum of the system can be moreeffectively corrected, enabling the focal plane to become more flat nearthe periphery. When the third lens element has positive refractivepower, the high order aberrations of the system can be favorablycorrected.

In the aforementioned imaging lens system, the on-axis spacing betweenthe first lens element and the second lens element is T12, the focallength of the imaging lens system is f, and they satisfy the relation:0.5<(T12/f)×100<15. The above relation can prevent the astigmatism frombecoming too large.

In the aforementioned imaging lens system, it is preferable that thesecond lens element has a concave image-side surface so as toeffectively lengthen the back focal length of the imaging lens system,thereby providing sufficient space between the fifth lens element andthe image plane to accommodate other components.

In the aforementioned imaging lens system, it is preferable that thethird lens element has a convex object-side surface so that the highorder aberrations of the system can be favorably corrected to improvethe image quality. Preferably, the fourth lens element has a concaveobject-side surface and a convex image-side surface so that theastigmatism of the system can be effectively corrected.

In the aforementioned imaging lens system, the Abbe number of the firstlens element is V1, the Abbe number of the second lens element is V2,and they preferably satisfy the relation: V1−V2>20, thereby thechromatic aberration can be effectively corrected. And it will be morepreferable that V1 and V2 satisfy the relation: V1−V2>30.

In the aforementioned imaging lens system, the focal length of theimaging lens system is f, the focal length of the first lens element isf1, and they preferably satisfy the relation: 1.0<f/f1<1.8. When theabove relation is satisfied, the refractive power of the first lenselement is more balanced so that the total track length of the systemcan be effectively reduced. The above relation also prevents the highorder spherical aberration from becoming too large, so that the imagequality can be improved. And it will be more preferable that f and f1satisfy the relation: 1.2<f/f1<1.6.

In the aforementioned imaging lens system, the focal length of thefourth lens element is f4, the focal length of the fifth lens element isf5, and they preferably satisfy the relation: −1.5<f4/f5<−0.5. The aboverelation ensures the telephoto structure formed by the fourth and fifthlens elements and facilitates reducing the total track length of thesystem.

In the aforementioned imaging lens system, it is preferable that, of thethird, fourth and fifth lens elements, all lens elements which aremeniscus in shape satisfy the relation: 0.5<R_(o)/R_(i)<2.0, whereinR_(o) represents the radius of curvature of the object-side surface ofthe meniscus lens element and R_(i) represents the radius of curvatureof the image-side surface of the meniscus lens element. The aboverelation effectively reduces the sensitivity of the system by preventingthe refractive power of the meniscus lens elements from becoming toolarge.

In the aforementioned imaging lens system, the radius of curvature ofthe object-side surface of the first lens element is R1, the focallength of the imaging lens system is f, and they preferably satisfy therelation: 0.2<R1/f<0.4. When the above relation is satisfied, the totaltrack length of the imaging lens system can be effectively reduced. Theabove relation also prevents the high order aberrations from becomingtoo large.

In the aforementioned imaging lens system, the aperture stop is disposedbetween the imaged object and the first lens element so that thetelecentric feature is emphasized, resulting in a shorter total tracklength.

The aforementioned imaging lens system further comprises an electronicsensor on which an object is imaged. The on-axis spacing between theobject-side surface of the first lens element and the electronic sensoris TTL, half of the diagonal length of the effective pixel area of theelectronic sensor is ImgH, and they preferably satisfy the relation:TTL/ImgH<2.0. The above relation enables the imaging lens system tomaintain a compact form so that it can be equipped in compact portableelectronic products.

In the aforementioned imaging lens system, the radius of curvature ofthe image-side surface of the second lens element is R4, the focallength of the imaging lens system is f, and they preferably satisfy therelation: 0.7<R4/f<1.2. When the above relation is satisfied, thechromatic aberration of the system can be effectively corrected. Theabove relation also prevents the back focal length of the imaging lenssystem from becoming too long so that the system can maintain a compactform.

In the aforementioned imaging lens system, the Abbe number of the secondlens element is V2, the Abbe number of the third lens element is V3, andthey preferably satisfy the relation: |V2−V3|<15, thereby the chromaticaberration of the system can be effectively corrected.

The present invention provides another imaging lens system including, inorder from the object side to the image side: a first lens element withpositive refractive power having a convex object-side surface; a secondlens element with negative refractive power; a third lens element withnegative refractive power; a fourth lens element with positiverefractive power having a concave object-side surface and a conveximage-side surface; a fifth lens element with negative refractive powerhaving a concave image-side surface, at least one surface thereof beingprovided with at least one inflection point; and an aperture stopdisposed between an imaged object and the third lens element; whereinthe on-axis spacing between the first lens element and the second lenselement is T12, the focal length of the imaging lens system is f, andthey satisfy the relation: 0.5<(T12/f)×100<15.

In the aforementioned imaging lens system, the first lens element haspositive refractive power and a convex object-side surface so that thetotal track length of the imaging lens system can be effectivelyreduced; the second lens element has negative refractive power so thatthe chromatic aberration of the system can be favorably corrected; thethird lens element has negative refractive power so that the Petzval Sumof the system can be more effectively corrected, enabling the focalplane to become more flat near the periphery; the fourth lens elementhas positive refractive power so that the positive refractive power ofthe first lens element can be effectively distributed to reduce thesensitivity of the imaging lens system, and the concave object-sidesurface and the convex image-side surface thereof facilitate thecorrection of the astigmatism of the system; the fifth lens element withnegative refractive power and the fourth lens element with positiverefractive power form a telephoto structure, thereby the total tracklength of the imaging lens system can be effectively reduced.

In the aforementioned imaging lens system, the on-axis spacing betweenthe first lens element and the second lens element is T12, the focallength of the imaging lens system is f, and they satisfy the relation:0.5<(T12/f)×100<15. The above relation can prevent the astigmatism frombecoming too large.

In the aforementioned imaging lens system, it is preferable that thesecond lens element has a concave image-side surface so as toeffectively lengthen the back focal length of the imaging lens system,thereby providing sufficient space between the fifth lens element andthe image plane to accommodate other components.

In the aforementioned imaging lens system, it is preferable that thethird lens element has a convex object-side surface and a concaveimage-side surface so that the high order aberrations of the system canbe favorably corrected to improve the image quality.

In the aforementioned imaging lens system, the Abbe number of the firstlens element is V1, the Abbe number of the second lens element is V2,and they preferably satisfy the relation: V1−V2>30, thereby thechromatic aberration can be effectively corrected.

In the aforementioned imaging lens system, the focal length of theimaging lens system is f, the focal length of the first lens element isf1, and they preferably satisfy the relation: 1.0<f/f1<1.8. When theabove relation is satisfied, the refractive power of the first lenselement is more balanced so that the total track length of the systemcan be effectively reduced. The above relation also prevents the highorder spherical aberration from becoming too large, so that the imagequality can be improved. And it will be more preferable that f and f1satisfy the relation: 1.2<f/f1<1.6.

In the aforementioned imaging lens system, the focal length of thefourth lens element is f4, the focal length of the fifth lens element isf5, and they preferably satisfy the relation: −1.5<f4/f5<−0.5. The aboverelation ensures the telephoto structure formed by the fourth and fifthlens elements and facilitates reducing the total track length of thesystem.

In the aforementioned imaging lens system, it is preferable that, of thethird, fourth and fifth lens elements, all lens elements which aremeniscus in shape satisfy the relation: 0.5<R_(o)/R_(i)<2.0, whereinR_(o) represents the radius of curvature of the object-side surface ofthe meniscus lens element and R_(i) represents the radius of curvatureof the image-side surface of the meniscus lens element. The aboverelation effectively reduces the sensitivity of the system by preventingthe refractive power of the meniscus lens elements from becoming toolarge.

In the aforementioned imaging lens system, the radius of curvature ofthe object-side surface of the first lens element is R1, the focallength of the imaging lens system is f, and they preferably satisfy therelation: 0.2<R1/f<0.4. When the above relation is satisfied, the totaltrack length of the imaging lens system can be effectively reduced. Theabove relation also prevents the high order aberrations from becomingtoo large.

In the aforementioned imaging lens system, the aperture stop is disposedbetween the imaged object and the first lens element so that thetelecentric feature is emphasized, resulting in a shorter total tracklength.

The aforementioned imaging lens system further comprises an electronicsensor on which an object is imaged. The on-axis spacing between theobject-side surface of the first lens element and the electronic sensoris TTL, half of the diagonal length of the effective pixel area of theelectronic sensor is ImgH, and they preferably satisfy the relation:TTL/ImgH<2.0. The above relation enables the imaging lens system tomaintain a compact form so that it can be equipped in compact portableelectronic products.

In the present imaging lens system, the lens elements can be made ofglass or plastic material. If the lens elements are made of glass, thereis more freedom in distributing the refractive power of the system. Ifplastic material is adopted to produce lens elements, the productioncost will be reduced effectively. Additionally, the surfaces of the lenselements can be aspheric and easily made into non-spherical profiles,allowing more design parameter freedom which can be used to reduceaberrations and the number of the lens elements, so that the total tracklength of the imaging lens system can be reduced effectively.

In the present imaging lens system, if a lens element has a convexsurface, it means the portion of the surface proximate to the opticalaxis is convex; if a lens element has a concave surface, it means theportion of the surface proximate to the optical axis is concave.

Preferred embodiments of the present invention will be described in thefollowing paragraphs by referring to the accompanying drawings.

FIG. 1 shows an imaging lens system in accordance with a firstembodiment of the present invention, and FIG. 2 shows the aberrationcurves of the first embodiment of the present invention. The imaginglens system of the first embodiment of the present invention mainlycomprises five lens elements including, in order from the object side tothe image side: a plastic first lens element 100 with positiverefractive power having a convex object-side surface 101 and a concaveimage-side surface 102, the object-side and image-side surfaces 101 and102 thereof being aspheric; a plastic second lens element 110 withnegative refractive power having a convex object-side surface 111 and aconcave image-side surface 112, the object-side and image-side surfaces111 and 112 thereof being aspheric; a plastic third lens element 120with negative refractive power having a convex object-side surface 121and a concave image-side surface 122, the object-side and image-sidesurfaces 121 and 122 thereof being aspheric; a plastic fourth lenselement 130 with positive refractive power having a concave object-sidesurface 131 and a convex image-side surface 132, the object-side andimage-side surfaces 131 and 132 thereof being aspheric; and a plasticfifth lens element 140 with negative refractive power having a convexobject-side surface 141 and a concave image-side surface 142, theobject-side and image-side surfaces 141 and 142 thereof being aspheric,and each of which being provided with at least one inflection point;wherein an aperture stop 150 is disposed between an imaged object andthe first lens element 100; wherein the imaging lens system furthercomprises an IR filter 160 disposed between the image-side surface 142of the fifth lens element 140 and the image plane 170; and wherein theIR filter 160 has no influence on the focal length of the imaging lenssystem.

The equation of the aspheric surface profiles is expressed as follows:

${X(Y)} = {{\left( {Y^{2}/R} \right)/\left( {I + {{sqrt}\left( {1 - {\left( {1 + k} \right)*\left( {Y/R} \right)^{2}}} \right)}} \right)} + {\sum\limits_{i}{({Ai})*\left( Y^{i} \right)}}}$

wherein:

X: the height of a point on the aspheric surface at a distance Y fromthe optical axis relative to the tangential plane at the asphericsurface vertex;

Y: the distance from the point on the curve of the aspheric surface tothe optical axis;

k: the conic coefficient;

Ai: the aspheric coefficient of order i.

In the first embodiment of the present imaging lens system, the focallength of the imaging lens system is f, and it satisfies the relation:f=5.44.

In the first embodiment of the present imaging lens system, the f-numberof the imaging lens system is Fno, and it satisfies the relation:Fno=2.9.

In the first embodiment of the present imaging lens system, half of thefield of view of the imaging lens system is HFOV, and it satisfies therelation: HFOV=33.0 degrees.

In the first embodiment of the present imaging lens system, the on-axisspacing between the first lens element 100 and the second lens element110 is T12, the focal length of the imaging lens system is f, and theysatisfy the relation: (T12/f)×100=1.29.

In the first embodiment of the present imaging lens system, the Abbenumber of the first lens element 100 is V1, the Abbe number of thesecond lens element 110 is V2, and they satisfy the relation:V1−V2=32.5.

In the first embodiment of the present imaging lens system, the focallength of the imaging lens system is f, the focal length of the firstlens element 100 is f1, and they satisfy the relation: f/f1=1.41.

In the first embodiment of the present imaging lens system, the focallength of the fourth lens element 130 is f4, the focal length of thefifth lens element 140 is f5, and they satisfy the relation:f4/f5=−0.79.

In the first embodiment of the present imaging lens system, each of thethird lens element 120, the fourth lens element 130 and the fifth lenselement 140 is a meniscus lens element, wherein R_(o) represents theradius of curvature of the object-side surface of the meniscus lenselement, R_(i) represents the radius of curvature of the image-sidesurface of the meniscus lens element, and they satisfy the relations:R _(o) /R _(i)=1.09(the third lens element 120),R _(o) /R _(i)=1.27(the fourth lens element 130),R _(o) /R _(i)=1.73(the fifth lens element 140).

In the first embodiment of the present imaging lens system, the radiusof curvature of the object-side surface 101 of the first lens element100 is R1, the focal length of the imaging lens system is f, and theysatisfy the relation: R1/f=0.28.

In the first embodiment of the present imaging lens system, anelectronic sensor on the image plane 170 is provided for the imageformation of the imaged object. The distance on the optical axis betweenthe object-side surface 101 of the first lens element 100 and theelectronic sensor is TTL, half of the diagonal length of the effectivepixel area of the electronic sensor is ImgH, and they satisfy therelation: TTL/ImgH=1.66.

In the first embodiment of the present imaging lens system, the radiusof curvature of the image-side surface 112 of the second lens element110 is R4, the focal length of the imaging lens system is f, and theysatisfy the relation: R4/f=0.93.

In the first embodiment of the present imaging lens system, the Abbenumber of the second lens element 110 is V2, the Abbe number of thethird lens element 120 is V3, and they satisfy the relation:|V2−V3|=32.5.

The detailed optical data of the first embodiment is shown in FIG. 7(TABLE 1), and the aspheric surface data is shown in FIG. 8 (TABLE 2),wherein the units of the radius of curvature, the thickness and thefocal length are expressed in mm, and HFOV is half of the maximal fieldof view.

FIG. 3 shows an imaging lens system in accordance with a secondembodiment of the present invention, and FIG. 4 shows the aberrationcurves of the second embodiment of the present invention. The imaginglens system of the second embodiment of the present invention mainlycomprises five lens elements including, in order from the object side tothe image side: a plastic first lens element 300 with positiverefractive power having a convex object-side surface 301 and a concaveimage-side surface 302, the object-side and image-side surfaces 301 and302 thereof being aspheric; a plastic second lens element 310 withnegative refractive power having a convex object-side surface 311 and aconcave image-side surface 312, the object-side and image-side surfaces311 and 312 thereof being aspheric; a plastic third lens element 320with positive refractive power having a convex object-side surface 321and a concave image-side surface 322, the object-side and image-sidesurfaces 321 and 322 thereof being aspheric; a plastic fourth lenselement 330 with positive refractive power having a concave object-sidesurface 331 and a convex image-side surface 332, the object-side andimage-side surfaces 331 and 332 thereof being aspheric; and a plasticfifth lens element 340 with negative refractive power having a convexobject-side surface 341 and a concave image-side surface 342, theobject-side and image-side surfaces 341 and 342 thereof being aspheric,and each of which being provided with at least one inflection point;wherein an aperture stop 350 is disposed between an imaged object andthe first lens element 300; wherein the imaging lens system furthercomprises an IR filter 360 disposed between the image-side surface 342of the fifth lens element 340 and the image plane 370; and wherein theIR filter 360 has no influence on the focal length of the imaging lenssystem.

The equation of the aspheric surface profiles of the second embodimenthas the same format as that of the first embodiment.

In the second embodiment of the present imaging lens system, the focallength of the imaging lens system is f, and it satisfies the relation:f=5.46.

In the second embodiment of the present imaging lens system, thef-number of the imaging lens system is Fno, and it satisfies therelation: Fno=2.9.

In the second embodiment of the present imaging lens system, half of thefield of view of the imaging lens system is HFOV, and it satisfies therelation: HFOV=33.0 degrees.

In the second embodiment of the present imaging lens system, the on-axisspacing between the first lens element 300 and the second lens element310 is T12, the focal length of the imaging lens system is f, and theysatisfy the relation: (T12/f)×100=1.28.

In the second embodiment of the present imaging lens system, the Abbenumber of the first lens element 300 is V1, the Abbe number of thesecond lens element 310 is V2, and they satisfy the relation:V1−V2=32.5.

In the second embodiment of the present imaging lens system, the focallength of the imaging lens system is f, the focal length of the firstlens element 300 is f1, and they satisfy the relation: f/f1=1.42.

In the second embodiment of the present imaging lens system, the focallength of the fourth lens element 330 is f4, the focal length of thefifth lens element 340 is f5, and they satisfy the relation:f4/f5=−0.91.

In the second embodiment of the present imaging lens system, each of thethird lens element 320, the fourth lens element 330 and the fifth lenselement 340 is a meniscus lens element, wherein R_(o) represents theradius of curvature of the object-side surface of the meniscus lenselement, R_(i) represents the radius of curvature of the image-sidesurface of the meniscus lens element, and they satisfy the relations:R _(o) /R _(i)=0.97(the third lens element 320),R _(o) /R _(i)=1.05(the fourth lens element 330),R _(o) /R _(i)=1.48(the fifth lens element 340).

In the second embodiment of the present imaging lens system, the radiusof curvature of the object-side surface 301 of the first lens element300 is R1, the focal length of the imaging lens system is f, and theysatisfy the relation: R1/f=0.30.

In the second embodiment of the present imaging lens system, anelectronic sensor on the image plane 370 is provided for the imageformation of the imaged object. The distance on the optical axis betweenthe object-side surface 301 of the first lens element 300 and theelectronic sensor is TTL, half of the diagonal length of the effectivepixel area of the electronic sensor is ImgH, and they satisfy therelation: TTL/ImgH=1.66.

In the second embodiment of the present imaging lens system, the radiusof curvature of the image-side surface 312 of the second lens element310 is R4, the focal length of the imaging lens system is f, and theysatisfy the relation: R4/f=0.83.

In the second embodiment of the present imaging lens system, the Abbenumber of the second lens element 310 is V2, the Abbe number of thethird lens element 320 is V3, and they satisfy the relation:|V2−V3|=0.0.

The detailed optical data of the second embodiment is shown in FIG. 9(TABLE 3), and the aspheric surface data is shown in FIG. 10 (TABLE 4),wherein the units of the radius of curvature, the thickness and thefocal length are expressed in mm, and HFOV is half of the maximal fieldof view.

FIG. 5 shows an imaging lens system in accordance with a thirdembodiment of the present invention, and FIG. 6 shows the aberrationcurves of the third embodiment of the present invention. The imaginglens system of the third embodiment of the present invention mainlycomprises five lens elements including, in order from the object side tothe image side: a plastic first lens element 500 with positiverefractive power having a convex object-side surface 501 and a concaveimage-side surface 502, the object-side and image-side surfaces 501 and502 thereof being aspheric; a plastic second lens element 510 withnegative refractive power having a convex object-side surface 511 and aconcave image-side surface 512, the object-side and image-side surfaces511 and 512 thereof being aspheric; a plastic third lens element 520with positive refractive power having a convex object-side surface 521and a concave image-side surface 522, the object-side and image-sidesurfaces 521 and 522 thereof being aspheric; a plastic fourth lenselement 530 with positive refractive power having a concave object-sidesurface 531 and a convex image-side surface 532, the object-side andimage-side surfaces 531 and 532 thereof being aspheric; and a plasticfifth lens element 540 with negative refractive power having a convexobject-side surface 541 and a concave image-side surface 542, theobject-side and image-side surfaces 541 and 542 thereof being aspheric,and each of which being provided with at least one inflection point;wherein an aperture stop 550 is disposed between an imaged object andthe first lens element 500; wherein the imaging lens system furthercomprises an IR filter 560 disposed between the image-side surface 542of the fifth lens element 540 and the image plane 570; and wherein theIR filter 560 has no influence on the focal length of the imaging lenssystem.

The equation of the aspheric surface profiles of the third embodimenthas the same format as that of the first embodiment.

In the third embodiment of the present imaging lens system, the focallength of the imaging lens system is f, and it satisfies the relation:f=5.47.

In the third embodiment of the present imaging lens system, the f-numberof the imaging lens system is Fno, and it satisfies the relation:Fno=2.9.

In the third embodiment of the present imaging lens system, half of thefield of view of the imaging lens system is HFOV, and it satisfies therelation: HFOV=33.0 degrees.

In the third embodiment of the present imaging lens system, the on-axisspacing between the first lens element 500 and the second lens element510 is T12, the focal length of the imaging lens system is f, and theysatisfy the relation: (T12/f)×100=0.91.

In the third embodiment of the present imaging lens system, the Abbenumber of the first lens element 500 is V1, the Abbe number of thesecond lens element 510 is V2, and they satisfy the relation:V1−V2=32.5.

In the third embodiment of the present imaging lens system, the focallength of the imaging lens system is f, the focal length of the firstlens element 500 is f1, and they satisfy the relation: f/f1=1.45.

In the third embodiment of the present imaging lens system, the focallength of the fourth lens element 530 is f4, the focal length of thefifth lens element 540 is f5, and they satisfy the relation:f4/f5=−0.85.

In the third embodiment of the present imaging lens system, each of thethird lens element 520, the fourth lens element 530 and the fifth lenselement 540 is a meniscus lens element, wherein R_(o) represents theradius of curvature of the object-side surface of the meniscus lenselement, R_(i) represents the radius of curvature of the image-sidesurface of the meniscus lens element, and they satisfy the relations:R _(o) /R _(i)=0.98(the third lens element 520),R _(o) /R _(i)=1.05(the fourth lens element 530),R _(o) /R _(i)=1.42(the fifth lens element 540).

In the third embodiment of the present imaging lens system, the radiusof curvature of the object-side surface 501 of the first lens element500 is R1, the focal length of the imaging lens system is f, and theysatisfy the relation: R1/f=0.29.

In the third embodiment of the present imaging lens system, anelectronic sensor on the image plane 570 is provided for the imageformation of the imaged object. The distance on the optical axis betweenthe object-side surface 501 of the first lens element 500 and theelectronic sensor is TTL, half of the diagonal length of the effectivepixel area of the electronic sensor is ImgH, and they satisfy therelation: TTL/ImgH=1.66.

In the third embodiment of the present imaging lens system, the radiusof curvature of the image-side surface 512 of the second lens element510 is R4, the focal length of the imaging lens system is f, and theysatisfy the relation: R4/f=0.79.

In the third embodiment of the present imaging lens system, the Abbenumber of the second lens element 510 is V2, the Abbe number of thethird lens element 520 is V3, and they satisfy the relation:|V2−V3|=0.0.

The detailed optical data of the third embodiment is shown in FIG. 11(TABLE 5), and the aspheric surface data is shown in FIG. 12 (TABLE 6),wherein the units of the radius of curvature, the thickness and thefocal length are expressed in mm, and HFOV is half of the maximal fieldof view.

It is to be noted that TABLES 1-6(illustrated in FIGS. 7-12respectively) show different data of the different embodiments, however,the data of the different embodiments are obtained from experiments.Therefore, any imaging lens system of the same structure is consideredto be within the scope of the present invention even if it usesdifferent data. The preferred embodiments depicted above are exemplaryand are not intended to limit the scope of the present invention. TABLE7(illustrated in FIG. 13) shows the data of the respective embodimentsresulted from the equations.

What is claimed is:
 1. An imaging lens system including, in order froman object side to an image side: a first lens element with positiverefractive power having a convex object-side surface and a concaveimage-side surface; a second lens element with negative refractivepower; a third lens element; a fourth lens element having a conveximage-side surface; and a fifth lens element having an object-sidesurface and a concave image-side surface, the object-side and image-sidesurfaces thereof being aspheric, at least one surface thereof beingprovided with at least one inflection point; wherein the lens elementswith refractive power in the imaging lens system are only the first,second, third, fourth and fifth lens elements; a focal length of theimaging lens system is f, a focal length of the first lens element isf1, an Abbe number of the first lens element is V1, an Abbe number ofthe second lens element is V2, and the following relations aresatisfied:1.0<f/f1<1.8; andV1−V2>20.
 2. The imaging lens system according to claim 1, wherein theimaging lens system further comprises an aperture stop disposed betweenan imaged object and the first lens element.
 3. The imaging lens systemaccording to claim 2, wherein the fourth lens element has a concaveobject-side surface.
 4. The imaging lens system according to claim 2,wherein the second lens element has a convex object-side surface and aconcave image-side surface, and the object-side surface of the fifthlens element is convex.
 5. The imaging lens system according to claim 2,wherein the fourth lens element has positive refractive power and thefifth lens element has negative refractive power.
 6. The imaging lenssystem according to claim 1, wherein a focal length of the fourth lenselement is f4, a focal length of the fifth lens element is f5, and thefollowing relation is satisfied: −1.5<f4/f5<−0.5.
 7. The imaging lenssystem according to claim 1, wherein a radius of curvature of theobject-side surface of the first lens element is R1, and the followingrelation is satisfied: 0.2<R1/f<0.4.
 8. The imaging lens systemaccording to claim 1, wherein the following relation is satisfied:1.2<f/f1<1.6.
 9. The imaging lens system according to claim 1, whereinthe following relation is satisfied: V1−V2>30.
 10. The imaging lenssystem according to claim 1, wherein an Abbe number of the third lenselement is V3, and the following relation is satisfied: |V2−V3|<15. 11.The imaging lens system according to claim 1, wherein an on-axis spacingbetween the first lens element and the second lens element is T12, andthe following relation is satisfied: 0.5<(T12/f)×100<15.
 12. An imaginglens system including, in order from an object side to an image side: afirst lens element with positive refractive power having a convexobject-side surface and a concave image-side surface; a second lenselement with negative refractive power; a third lens element; a fourthlens element having a concave object-side surface and a conveximage-side surface; and a fifth lens element having an object-sidesurface and a concave image-side surface, the object-side and image-sidesurfaces thereof being aspheric, at least one surface thereof beingprovided with at least one inflection point; wherein the lens elementswith refractive power in the imaging lens system are only the first,second, third, fourth and fifth lens elements; an Abbe number of thefirst lens element is V1, an Abbe number of the second lens element isV2, and the following relation is satisfied: V1−V2>20.
 13. The imaginglens system according to claim 12, wherein the fourth lens element haspositive refractive power.
 14. The imaging lens system according toclaim 12, wherein the object-side surface of the fifth lens element isconvex.
 15. The imaging lens system according to claim 12, wherein afocal length of the imaging lens system is f, a focal length of thefirst lens element is f1, and the following relation is satisfied:1.0<f/f1<1.8.
 16. The imaging lens system according to claim 12, whereinan on-axis spacing between the first lens element and the second lenselement is T12, a focal length of the imaging lens system is f, and thefollowing relation is satisfied: 0.5<(T12/f)×100<15.
 17. The imaginglens system according to claim 12, wherein the imaging lens systemfurther comprises a stop disposed between an imaged object and the firstlens element.
 18. The imaging lens system according to claim 12, whereinan Abbe number of the third lens element is V3, and the followingrelation is satisfied: |V2−V3|<15.
 19. An imaging lens system including,in order from an object side to an image side: a first lens element withpositive refractive power having a convex object-side surface and aconcave image-side surface; a second lens element with negativerefractive power; a third lens element with negative refractive power; afourth lens element having a concave object-side surface and a conveximage-side surface; and a fifth lens element having an object-sidesurface and a concave image-side surface, the object-side and image-sidesurfaces thereof being aspheric, at least one surface thereof beingprovided with at least one inflection point; wherein the lens elementswith refractive power in the imaging lens system are only the first,second, third, fourth and fifth lens elements.
 20. The imaging lenssystem according to claim 19, wherein the fourth lens element haspositive refractive power and the fifth lens element has negativerefractive power.
 21. The imaging lens system according to claim 19,wherein a focal length of the fourth lens element is f4, a focal lengthof the fifth lens element is f5, and the following relation issatisfied: −1.5<f4/f5<−0.5.
 22. The imaging lens system according toclaim 19, an Abbe number of the first lens element is V1, an Abbe numberof the second lens element is V2, and the following relation issatisfied: V1−V2>20.
 23. The imaging lens system according to claim 19,wherein the object-side surface of the fifth lens element is convex. 24.The imaging lens system according to claim 19, wherein an on-axisspacing between the first lens element and the second lens element isT12, a focal length of the imaging lens system is f, and the followingrelation is satisfied: 0.5<(T12/f)×100<15.
 25. The imaging lens systemaccording to claim 19, wherein an Abbe number of the second lens elementis V2, an Abbe number of the third lens element is V3, and the followingrelation is satisfied: |V2−V3|<15.